Fix freeing of response objects in client API

This commit simple adds an hattach() call to the co_free() function in the client API. This explicitly detaches the object that is being freed from the memory pool. Otherwise, it will not be freed with this call and will not be until the API is shut down.

To test, there should not be any obvious change of functionality from this simple fix. You should just verify that interactive client commands still work properly, and that the client does not bomb out (the commotion CLI client uses this API to free responses when in interactive mode).